Resource allocation in multi-stream IP network for optimized quality of service

ABSTRACT

A resource allocation of multiple compressed AV streams delivered over the Internet is disclosed that achieves end-to-end optimal quality through a multimedia streaming TCP-friendly transport (MSTFP) protocol that adaptively estimates the network bandwidth while smoothing the sending rate. Resources allocated dynamically according to a media encoding distortion and network degradation algorithm. A scheme is also disclosed for dynamically estimating the available network bandwidth for streaming of objects, such as MPEG4 multiple video objects, in conjunction with the MSTFP protocol. The scheme can account for packet-loss rates to minimize end-to-end distortion for media delivery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This US Non-Provisional Patent Application is a Continuation Applicationof prior Ser. No. 09/865,941, now U.S. Pat. No. 7,260,826, filed 25 May2001, which claims the benefit of priority to U.S. Provisional PatentApplication No. 60/208,659, filed on 31 May 2000. U.S. Pat. No.7,260,826 and Patent application 60/208,659 are hereby incorporated byreference in their entirety herein.

TECHNICAL FIELD

The present invention relates to systems and methods for streaming media(e.g., video and audio) over a network, such as the Internet.

BACKGROUND OF THE INVENTION

With the success of the Internet and growing network resources, audioand video streaming is of enormous interest among Internet multimediaapplications. Recently, tools such as RealPlay™ software and MicrosoftNetShow® software have been developed to stream media content over anetwork. There remain, however, challenges to the streaming of mediaover the IP-based Internet due to issues such as the lack of a qualityof service (QoS) guarantee, bandwidth variations, packet-losses, delaysvarying from time to time, and unknown network characteristics.

Since the Internet is a shared environment and does not micro-manageutilization of its resources, end systems are expected to be cooperativeby reacting to congestion properly and promptly. As a result, overallutilization of the network remains high while each flow obtains a fairshare of resources. Unfortunately, many of the current commercialstreaming applications do not behave in a network-friendly fashion.

The available bandwidth in the Internet fluctuates frequently in nature.Most conventional streaming applications are unable to perform qualityadaptation as available bandwidth changes, especially quality adaptationamong multiple streams. Thus, these conventional streaming applicationsdo not make effective use of the bandwidth.

To date several schemes have been developed for QoS management such asresource reservation, priority mechanism, and application level control.Prior art QoS management schemes and other background information,referred to elsewhere in the document, are presented in the followingpublications, each of which is incorporated herein by reference inentirety:

1. R. Braden, L. Zhang, S. Berson et al, “Resource ReSerVation Protocol(RSVP)—Version 1 Functional Specification”, RFC 2205, September 1997(“hereinafter, “Braden et al.”);

2. R. Rejaie, M. Handley, and D. Estrin, “Quality adaptation forcongestion controlled video playback over the Internet”, Proceedings ofSIGCOM 99 (“hereinafter, “Rejaie et al. [SIGCOM]”);

3. R. Rejaie, M. Handley, and D. Estrin, “An end-to-end rate-basedcongestion control mechanism for realtime streams in the Internet”,Proceedings of INFOCOMM 99, 1999 (“hereinafter, “Rejaie et al.[INFOCOMM]”);

4. T. Chiang and Y. Q. Zhang, “A new rate control scheme using quadraticrate-distortion modeling”, IEEE Trans. Circuits Syst. Video Technol.,February 1997 (“hereinafter, “Chiang et al.”);

5. D. Sisalem and H. Schulztinne, “The loss-delay based adjustedalgorithm: A TCP-friendly adaptation scheme”, Proceedings of NOSSDAV'98,1998 (“hereinafter, “Sisalem et al.”);

6. J. Padhye, V. Firoiu, D. Towsley and J. Kurose, “Modeling TCPthroughput: A simple model and its empirical validation”, Proceedings ofSIGCOMM'98, 1998 (“hereinafter, “Padhye et al.”);

7. O. Verscheure, P. Frossard and M. Hamdi, “MPEG-2 video services overpacket networks: joint effect of encoding rate and data loss onuser-oriented QoS”, Proceedings of NOSSDAV 98, 1998 (“hereinafter,“Verscheure et al.”);

8. A. Vetro, H. F. Sun and Y. Wang. “MPEG-4 rate control for multiplevideo objects”. IEEE Trans. Circuits Syst. Video Technol., February 1999(“hereinafter, “Vetro et al.”); and

9. M. Eckert and J. I. Ronda. “Bit-rate allocation in multi-object videocoding”. ISO/IEC JTC1/SC29/WG11 MPEG98/m3757, Dublin, Ireland(“hereinafter, “Eckert et al.”).

Among the foregoing QoS management schemes, resource reservation forsupporting a certain QoS level, which was proposed by Braden et al., isthe most straightforward approach. However, since it is difficult toknow the characteristics of a stream in advance, one may tend toover-allocate resources in order to guarantee the requested QoS level,leading to network under-utilization. Besides that, the most challengingissue for the resource reservation mechanism is that it is bothdifficult and complex to implement and to deploy.

In priority mechanisms, different data packets or streams are labeledwith different priorities and thereby treated differently at the networkrouters. While this approach is simple, the exact mechanism for settingthe priority levels, the router mechanism for controlling these levels,and the actual gain are unclear.

In application level control scheme, the QoS is controlled by adaptingthe sender transmission rate as was taught by Rejaie et al. [SIGCOM] andChiang et al. Most of the control algorithms, however, randomlydistribute resources among multiple streams without a globalcoordination mechanism. In order to employ a global coordination scheme,traffic control is usually adopted. There are several TCP-friendly rateadjustment protocols that have been reported recently. It has beenproposed that transport protocols, including those taught by Rejaic etat. [INFOCOMM] and Sisalem et al. who teach transport protocols wherethe throughput of a long-lived TCP connect is calculated based on theTCP characterization. However, Padhye et al. demonstrated that the aboveapproaches to calculating the throughput are not accurate in cases wherethe packet-loss rate is higher than five percent (5%). Since thisapproach does not account for retransmission timeouts, it usuallyoverestimates the throughput of a connection as the packet-loss rateincreases.

Other challenges to streaming video include network bandwidthadaptation, media adaptation, and error resilience. Network bandwidthadaptation deals with dynamic network bandwidth estimation, while mediaadaptation controls the media bit rate according to the networkconditions. Error resilience refers to the ability to track, localizeand recover transmission errors.

Without bandwidth adaptation, video transmission tends to competeunfairly with other TCP traffic, causing network congestion andresulting in a lower transmission rate for other TCP traffic. Inaddition, congestion collapse occurs when the aggregate bandwidth of themedia traffic exceeds the network capacity. In order to dynamicallyadjust the transmission rate while co-existing with other TCP-basedapplications, several congestion control protocols have been proposed toadapt the sending rate in such a way that congested bandwidth is shared“fairly” with TCP applications. The majority of these protocols arebased on TCP characterizations. Specifically, in the absence ofretransmission time-outs, the steady state throughput of a long-livedTCP connect is given by:

$\begin{matrix}{{{Throughput} = \frac{C}{R*\sqrt{p}}},} & (1)\end{matrix}$where C is a constant that is usually set to either 1.22 or 1.31,depending on whether the receiver uses delayed acknowledgments, R is theround trip time experienced by the connection, and p is the expectednumber of window reduction events per packet sent. Since Equation (1)does not account for retransmission timeouts, it usually overestimatesthe connection throughput as packet-loss rate increases. It is has beenreported that Equation (1) is not accurate for packet-loss rates higherthan 5%.

MPEG-4 is an object-based coding standard in which a visual scenetypically has several video objects (VOs), each characterized by itsshape, motion, and texture. The VOs are coded into separate bit streamsthat can be individually accessed and manipulated. The compositioninformation is sent in a separate stream. To date several prior art ratecontrol algorithms have been proposed. One such rate control algorithmwas proposed by Chiang et al. for a single VO using a quadraticrate-quantizer model as the baseline rate control scheme used in theMPEG4 standard. This rate control scheme was extended by Vetro et al. tomultiple video objects (MVOs). As taught by both Chiang et al. and Vetroet al., the total target bit rate for all objects is controlled by a“joint-buffer” and allocated proportionally to the motion, size, andsquare of MAD (mean absolute distortion). For MVOs, Eckert et al. taughtseveral straightforward approaches based upon the video objectimportance level. Although these approaches allow different objects tobe encoded at different frame rates, when put in one scene, theseobjects with different frame rates may cause a break in the compositioninformation and can result in unacceptable video reconstruction.

When MPEG-4 video is transported over the Internet, all the above ratecontrol schemes could not work well since they do not adapt to networkbandwidth and packet-loss conditions that vary from time to time. Thus,the available resources could not be efficiently utilized and sometimesthey may suffer from heavy congestion.

It would be an advance in the art to devise a multimedia streamingTCP-friendly transport protocol that can adaptively estimate the networkbandwidth and smooth the sending rate. It would also be an advance inthe art to devise a global resource allocation control mechanism thatmaximizes the quality of AV streams delivered across fairly congestedconnections, where bits are allocated dynamically according to the mediaencoding distortion and network degradation. With respect to multiplevideo objects, it would be an advance in the art to devise a ratecontrol scheme that uses such a multimedia streaming TCP-friendlyprotocol while minimizing the overall distortion under the constraintthat the total rate for all objects is upper-bounded by a target bitrate. Finally, an advance in the audiovisual streaming art would beachieved by minimizing the end-to-end distortion for a given networktraffic condition and picture quality requirement.

BRIEF SUMMARY OF THE INVENTION

The resource allocation architecture allocates resources among multiplemedia streams over a network (such as the Internet) to achieve optimizedend-to-end quality of service. Examples of the media include audio,MPEG/H.26× compressed video, mesh, compressed image, and so forth. Theresource allocation architecture copes with packet drops and fluctuatingavailable bandwidth. From the network congestion control viewpoint, thearchitecture allows a multimedia streaming TCP-friendly protocol, whichis suitable for multimedia streaming. From the visual quality controlviewpoint, the architecture provides a way to maximize the visualquality for all streams based on the variable available bandwidth andthe characteristics of each of the multiple media streams. The resourceallocation architecture thereby enables the user to gain globallyoptimized quality at the client side.

A method is disclosed for transmitting a mixed media data stream,including audio and multiple video objects (MVOs), between a sender anda receiver through a connection over a network. The transmissioncharacteristics of the connection between server and receiver aremonitored and the available bandwidth is estimated at the sender basedupon the transmission characteristics of the connection monitored at thereceiver side. A global buffer is allocated for the mixed media datastream to be transmitted from the sender to the receiver as a functionof the estimated available bandwidth at the sender. A portion of eachVideo Object Plane (VOP) in the global buffer is pre-encoded withrespect to a quantization parameter (QP) of the VOP. The VOP in theglobal buffer is then encoded based on the QP. An update is performed toa rate distortion model based upon the QP and a frame skipping functionis performed after the VOP encoding. The sender then transmits theencoded video object plane in the global buffer at a regulated sendertransmission rate from the sender as a function of the estimatedavailable bandwidth at the sender.

In one implementation, a multimedia streaming TCP-friendly transportprotocol is used to adaptively estimate the network bandwidth and smooththe rate at which a server sends streaming data to a receiver. A globalresource allocation control mechanism is also implemented. Thisallocation control maximizes the quality of audio-visual (AV) streamsdelivered across congested connections, where bits are allocateddynamically to a global buffer for transmission over a network. Thisdynamic bit allocation is made in a manner that minimizes the mediaencoding distortion and network degradation.

In an implementation dealing with multiple video objects, a rate controlscheme uses a TCP-friendly protocol that minimizes the overalldistortion under the constraint that the total rate for all objects isupper-bounded by a target bit rate. The TCP-friendly protocol is used toobtain network characteristics, including packet-loss rate, delay andjitter. Network characteristics are used to estimate available networkbandwidth and to make adjustments to the sending rate in a smooth,non-erratic manner. The sending rate control scheme implemented hereinallows the target bit rate and global buffer size to be dynamicallyadapted to the estimated available network bandwidth. Additionally, thepacket-loss rate is taken into account when calculating the overalldistortion.

In each implementation, end-to-end distortion is minimized for networktraffic conditions and picture quality requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a general architecture where several continuous mediaservers play back AV streams for heterogeneous clients on demand overthe Internet, where each server is able to support a large number ofrequests simultaneously, and where each client is able to requestservices from different servers.

FIG. 2 depicts an end-to-end framework for media streaming over theInternet.

FIG. 3 depicts the Gilbert Model which is able to capture the dependencebetween consecutive packet-losses, and wherein “1” is the received stateand “0” is the loss state.

FIG. 4 illustrates a topology used in a simulation of an implementationof a resource allocation scheme.

FIGS. 5 and 6 show simulation results of the throughput and sendingrate, respectively, for six (6) different connections with theirrespective times.

FIG. 7 is a plot of peak signal to noise ratio (PSNR) per frame ofdifferent video objects, wherein the plot is illustrated with andwithout the disclosed resource allocation control scheme.

FIG. 8 is a plot of the PSNR per frame using two of the four objects inthe MPEG-4 test sequence “Coast Guard”, wherein the plot is illustratedwith and without the disclosed resource allocation control scheme.

FIG. 9 shows a block diagram of the network resource allocation schemedisclosed herein for multiple video objects (MVOs).

FIG. 10 shows the simulation results of the network available bandwidthand its estimation in a network conditions plot of bandwidth againsttime, wherein these two curves depict the real available bandwidthvalues and the estimated values obtained by using the multimediastreaming TCP-friendly transport protocol.

FIGS. 11 and 12 both illustrate the disclosed network adaptive ratecontrol scheme and the convention MPEG-4 Q2 scheme, where each show aplot of PSNR per frame, where FIG. 11 uses the MPEG-4 “coast guard” testsequence, and where FIG. 12 uses the MPEG-4 “news” test sequence.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following discussion describes a system and method to allocatenetwork resources among multiple media streams. These network resourcesare allocated within a client-network-server framework (such as theInternet) in a TCP-friendly manner to achieve optimized end-to-endquality of service. Simulation results are given that depict animplementation of the allocation of network resources to yield optimizedend-to-end quality of service. A final discussion is then presented ofan implementation of a network adaptive rate control scheme, includingthe results of a simulation of the same.

1. Framework for Internet Audio-Visual Streaming

In media streaming, multiple servers and multiple clients are usuallyemployed in the same session. FIG. 1 depicts a general architecturewhere several continuous media servers play back AV streams forheterogeneous clients on demand, in which Server₁, Server_(i),Server_(j), Server_(n) are in communication with Client₁, Client_(p),Client_(q), and Client_(m) through the Internet. Each server is able tosupport a large number of requests simultaneously and each client isable to request services from different servers.

FIG. 2 depicts an implementation of an end-to-end framework for mediastreaming over the Internet seen at reference numeral 220. End-to-endtransport control is adopted by using a Multimedia StreamingTCP-Friendly transport Protocol (MSTFP) seen at reference numerals 212and 232. The MSTFP protocol is a rate-based TCP-friendly protocol thatcontinuously monitors the connection between sender and receiver, whichare depicted in FIG. 2, respectively, as Server 210 and Client 230. Theresults of the continuous monitoring of the connection are then used toregulate the bit transmission rate of Server 210.

A Quality of Service (QoS) Adaptation and Global Resource AllocationControl module 214 adjusts the quality of the bit stream that istransmitted from server 210 to client 230 through Internet 220. Module214 periodically estimates the available bandwidth from the MSTFPprotocol as derived from module 212. Combining this information with themedia characteristics of media streams Videom, Videon, and Audiok,module 214 adjusts the quality of the total transmitted streams byresource reallocation in a Global Buffer Control module 216 at Server210. Data occupying the global buffer is transmitted from Server 210 inthe MSTFP protocol at module 212 through Internet 220 to Client 230.

Client 230 processes the MSTFP protocol at module 232 and passes themedia to a demultiplexer module seen in FIG. 2 at reference numeral 234.Demultiplexer module 234 demultiplexes the combined stream into originalmedia types for decoding at Videom decoder, Videon decoder, and Audiokdecoder. The output from the video and audio decoders are mixed at aMedia Mixer module 236 and output to an output device 238, such as apersonal computer at Client 230 having a display device and having asound card with associated speakers.

A discussion of the MSTFP protocol follows. Then, two exemplaryimplementations that use the MSTFP protocol are set forth. The firstimplementation is a resource allocation scheme for audio-visualstreaming that is discussed in conjunction with the example illustratedin FIG. 2. The second implementation is a network adaptive sending ratecontrol scheme that is discussed in conjunction with the exampleillustrated in FIG. 9. Both implementations will be discussedconceptually and in a presentation of results obtained by respectiveexperimentations of each.

2. MULTIMEDIA STREAMING TCP-FRIENDLY TRANSPORT PROTOCOL (MSTFP) Totransmit the video and audio streams over the Internet, thecharacteristics of packetloss and bandwidth fluctuation should be takeninto account. The multimedia streaming TCP-friendly protocol (MSTFP)intends to minimize the number of future packets likely to be droppedand then smoothes the sending rate. Integral to the MSTFP protocol isthe underlying TCP model taught by Padhye et al. which allows the senderto change its sending rate based on the observed packet-loss rate, roundtrip times, and retransmission time-outs. The two main characteristicsof the MSTFP protocol are “TCP-friendliness” and “rate smoothness”.

The MSTFP protocol involves sender-side data packets and receiver-sidecontrol packets. The sender sends data packets to the receiver at acertain rate. The header of the sender-side packet includes the packetsequence number, a timestamp indicating the time when the packet is sent(ST1), and the size of the sending packet. The receiver sends feedbackto the sender at regular intervals. The receiver-side packet includesthe time interval that the packet spent in the receiver side (ΔRT), thetimestamp of the packet sent from the sender (ST1), the estimatedpacket-loss rate, and the rate at which data is received. Based on thereceiver's feedback, the sender uses the TCP model taught by Padhye etal. to adjust its sending rate in a TCP-friendly manner.

What follows is a discussion of packet-loss rate estimation, round triptime estimation (RTT), retransmission time-out estimation (TO),available bandwidth estimation, and sending rate adjustment, each ofwhich apply to the MSTFP protocol. The MSTFP protocol is preferred forthe resource allocation implementation for audio-visual streaming andfor the network adaptive sending rate control implementation.

A. Packet-loss Rate Estimation

A two-state Markov Model (Gilbert model) is used to model thepacket-loss in the network. FIG. 3 depicts the Gilbert Model, wherein“1” is the received state and “0” is the loss state. This model is ableto capture the dependence between consecutive losses. Network packetscan be represented as a binary time series, {x_(i)}_(i=1) ^(n), wherex_(i) takes 1 if the ith packet has arrived successfully and 0 if it islost. The current state, X_(i), of the stochastic process depends onlyon the previous value, X_(i-1). The transition probabilities between thetwo states are calculated as follows:p=P[X _(i)=1|X _(i-1)=0] and q=P[X _(i)=0|X _(i-1)=1].  (2)

The maximum likelihood estimators of p and q for a sample trace are:

$\begin{matrix}{{\hat{p} = {{{n_{01}/n_{0}}\mspace{14mu}{and}\mspace{14mu}\hat{q}} = {n_{10}/n_{1}}}},} & (3)\end{matrix}$where n₀₁ is the number of times in the observed time series when 1follows 0 and n₁₀ is the number of times when 0 follows 1. n₀ is thenumber of 0s and n₁ is the number of 1s in the trace.

The probability of the event that the trace is in the loss state isgiven by:

$\begin{matrix}{P_{L} = {\frac{\hat{q}}{\hat{p} + \hat{q}}.}} & (4)\end{matrix}$

To obtain an accurate and stable measurement of the packet loss rate,the scheme uses a filter that weights the n (n=8 in this implementation)most recent packet loss rate values in such a way that the measuredpacket loss rate changes smoothly. Thus, the estimated packet loss ratein the ith time interval is calculated as:

$\begin{matrix}{P_{L,i} = {\sum\limits_{j = 0}^{n - 1}\left( {w_{j} \times \overset{\_}{P_{L,{i - j}}}} \right)}} & (5)\end{matrix}$where P_(L,i-j) is the measured packet loss rate in the (i-j)th timeinterval.

It can be seen that the weighting parameters values, wj, used incalculating the packet loss rate determines the protocol's speed inresponding to changes in the level of congestion. Two sets of weightingparameters are defined in this implementation, which are denoted as WS1and WS2, respectively.

W0 W1 W2 W3 W4 W5 W6 W7 WS1 1.0 1.0 1.0 1.0 0.8 0.6 0.4 0.2 WS2 1.2 1.21.0 10 0.8 0.5 0.3 0.1

In the above two parameter sets, WS1 is used in the default cases. Whenthe most recent packet loss rate is less than the half of the calculatedpacket loss rate, WS2 is adopted to concentrate more of the relativeweight on the most recent packet loss rate.

B. RTT and TO Estimation

Based on the receiver's feedback packet, the sender can adjust thecurrent RTT using the following equation.RTT=α× RTT +(1−α)×(now−ST1−ΔRT),   (6)where RTT is the current round trip time, RTT is the estimated roundtrip time, now is the timestamp indicating the time at which the packetwas received in the sender, and a is a weighting parameter that is setto 0.75 to smooth the variation for the purposes of this implementation.

After calculating the RTT, retransmission timeout can be defined as:TO=RTT+(k×RTTVAR),   (7)where k is a constant that is recommended to take the value 4, RTT isthe estimated round trip time of the sender packet from the sender tothe receiver, and RTTVAR is a smoothed estimate of the variation of RTT.RTTVAR in Eq. (7) can be represented as:RTTVAR=α ₂ × RTTVAR+(1−α₂)×|RTT−(now−ST1−ΔRT)|.   (8)In Eq. (8), RTTVAR is the current variation in the round trip time ofthe sender packet from the sender to the receiver (RTT), α2 is aweighting parameter that is preferably set to 0.75, and RTTVAR is asmoothed estimate of RTTVAR.

C. Available Bandwidth Estimation

After the above procedures, the sender can estimate the presentavailable network bandwidth as taught by Padhye et al. who calculate thepresent available network bandwidth as follows:

$\begin{matrix}{{{rcvrate} = \frac{PacketSize}{{{RTT} \times \sqrt{2{P_{L}/3}}} + {3 \times {TO} \times P_{L} \times \sqrt{3{P_{L}/8}} \times \left( {1 + {32P_{L}^{2}}} \right)}}},} & (9)\end{matrix}$where PacketSize is the size of the sending packet and TO is a Time Outperiod that indicates the length of a time interval before which asender should wait before re-transmitting a packet of data. As taught byPadhye et al., the present implementation proposes a TCP protocol thatcalculates TO without re-transmitting the data.

D. Sending Rate Adjustment

After estimating the available network bandwidth, the sender candynamically adjust its sending rate. TCP congestion control is based onAdditive Increase/Multiplicative Decrease (AIMD), which is independentof the lost fraction and adjusting interval. An alternate way to changethe sending rate related to current packet-loss is described as:if (rcvrate> currate) multi=(now−lastchange)/RTT constraint multi from 1to 2 currate=currate+(PacketSize/RTT)×multi   (10)elsecurrate=β×rcvrate+(1−β)× currate,where currate is the present sending rate, currate is the updatedsending rate, lastchange is the timestamp indicating the time at whichlast adjustment occurred, and β is the weighting parameter that is setto 0.75 in this implementation. An advantage of the above scheme is thatthe sending rate can be increased dramatically to the availablebandwidth, and in the meanwhile the rate can be decreased smoothly. Inother words, the MSTFP protocol has less variation in the transmissionrate and is less sensitive to random loss caused by channel error.

3. Resource Allocation for Audio-Visual Streaming

What follows is a discussion of an implementation of a resourceallocation scheme for audio-visual streaming and a presentation of theresults of simulations of the same.

Dynamic resource allocation is preferable for distributed multimediasystems that support application-level control. In the exampleillustrated in FIG. 2, dynamic resource allocation can be implemented byintegrating global buffer control 216 with Quality of Service Adaptationand Global Resource Allocation Control 216 using dynamic networkbandwidth estimation. Dynamic network bandwidth estimations are madeusing the changing characteristics of Internet 220 learned at modules212 and 232 using the MSTFP protocol. One of the most challenging tasksof dynamic resource reallocation is global coordination of the feedbackinformation from multiple streams.

Different applications, such as file-transfer, web browsing, and AVstreaming, have different tolerances that can be mismatched between thesending rate and the network bandwidth. For example, file-transfer hasno real-time constraints and is tolerable to delay. The differencebetween the sensitivities to human aura and visual systems indicates theaudio and video should be handled differently when adverse conditionsarise, thereby affecting the playback of media streams. It is well knownthat the aural sense is more sensitive to disturbances than the visualsense. Therefore, it is appropriate to assign higher priority to audiodata than video data. If data can be discarded when congestion occurs inthe network, it is preferable to discard video data first.

In general, the objective of resource allocation is to minimize theoverall distortion under the total bit-rate constraint. If the sendingrate of the ith media stream is denoted as r_(i), the distortion of ithmedia as d_(i), and the quality-impact parameter of this stream asα_(i), then a minimization of the distortion can be expressed as:

$\begin{matrix}{{{{Minimize}\mspace{14mu} D} = {\sum\limits_{i}{\alpha_{i} \times d_{i}}}},{{{subject}\mspace{14mu}{to}\mspace{14mu} R} = {{\sum\limits_{i}r_{i}} \leq R_{T}}},} & (11)\end{matrix}$where R_(T) is the total bit budget for the current time instantobtained from the MSTFP protocol, i.e.,

$\begin{matrix}{R_{T} = {\sum\limits_{i}{{currate}_{i}.}}} & (12)\end{matrix}$

In the resource allocation scheme disclosed below, the main focus is onglobal buffer control and bandwidth allocation, where a global buffer isused to control the bit rate allocation. Using the MSTFP protocol, thecurrent available network bandwidth R_(T), can be estimated. Togetherwith the number of bits spent in the global buffer in the previous timeinstant B_(prev), the size R_(old)/2, and the occupancy of the globaloutput buffer W_(prev) in the previous time instant, the target rate andglobal buffer can be updated for each time interval. The output targetrate of the joint buffer control is allocated among each stream to yieldthe target bit for an individual object. As the buffer size R_(old)/2 ischanged to R_(T)/2, the occupancy of the buffer is changed as follows:W _(cur)=max(((W _(prev) +B _(prev))×R _(T) /R _(old) −R _(T) /F),0).  (13)where “F” is the video frame rate (e.g., 20 frame/second, 30frame/second, etc.)

To achieve the global minimal distortion among the multiple streams, itis desirable to define the appropriate function for rate and distortion.

To predict the number of bits that is used to encode the current streamfor video objects, a quadratic function calculation is used that istaught by Chiang et al., and is given by:

$\begin{matrix}{r_{i} = {\frac{p_{i\; 1} \times {MAD}_{i}}{Q_{i}} + \frac{p_{i2} \times {MAD}_{i}}{Q_{i}^{2}}}} & (14)\end{matrix}$

Verscheure et al. teach that packet-loss has an impact on video quality.For video distortion measuring, the present implementation considers thepacket-loss that occurs during video transmission. The video qualitywill drop quickly as the packet-loss rate and the sending rate go up.

To take the packet-loss into account, the implementation uses anotherquadratic function to estimate the distortion that is given by:d _(i) =q _(i1) ×Q _(i) +q _(i2) ×Q _(i) ² +q _(i3) ×r _(i) ×P _(L) _(i).  (15)

In the audio case, one could still use the above distortion and ratecontrol algorithms, respectively, in Eqs. (14) and (15). In Eq. (14),MAD_(i) is the energy for the audio case.

Having the information of the rate and distortion, distortion can beminimized by Lagrange optimization to obtain the appropriatequantization parameters. These estimated quantization parameters areused in the encoding process.

B. Simulation Results

MPEG-4 streams with multiple video objects were used in a simulation todemonstrate the effectiveness of an implementation of the networkresource allocation scheme for audio-visual streaming. MPEG-4 is anobject-based video coding standard in which a visual scene is typicallycomposed of Video Objects (VOs). Each VO is individually coded to giverise to an elementary bit stream that can be individually accessed andmanipulated. The composition information is sent in a separate stream.For multiple video object streams, foreground objects receive mostattention from the viewer, while background objects are of lessimportance. In addition, foreground objects usually change rapidly,while background objects change slowly. Therefore, they may havedifferent impact on the overall video quality.

In the simulation, the Network Simulator (NS) version 2 software wasused to study the MSTFP protocol and the resource allocation mechanismfor the MPEG-4 multiple video objects. The main tasks of the simulationwere to select appropriate network topologies, effectively model thebackground traffic, and define proper performance metrics.

FIG. 4 is a topology used in the simulation. The topology has a singleshared bottleneck link. The sources or senders are on one side of thelink in FIG. 4 and the receivers are on the other side. All links exceptthe bottleneck link are sufficiently provisioned to ensure that anydrops/delays that occurred are only caused by congestion at thebottleneck link. All links are drop-tail links. In the simulation, thebackground traffic has infinite-duration TCP-like connections andinfinite-duration real-time adaptive protocol (RAP) connections thatwere proposed by Rejaie et al. [SIGCOM] to deliver real-time trafficover Internet.

As used herein, “friendliness” metrics are used as follows. k_(m)denotes the total number of monitored MSTFP protocol connections andk_(t) denotes the total number of monitored TCP connections. Thethroughputs of the MSTFP protocol connections are further denoted as T₁^(m), T₂ ^(m), . . . , T_(k) _(m) ^(m) and the throughputs of the TCPconnections as T₁ ^(t), T₂ ^(t), . . . , T_(k) _(l) ^(t). Then theaverage throughputs of the MSTFP protocol and TCP connections arerespectively defined as follows:

$\begin{matrix}{T_{M} = {{\frac{\sum\limits_{i = 1}^{k_{m}}T_{i}^{m}}{k_{m}}\mspace{14mu}{and}\mspace{14mu} T_{T}} = {\frac{\sum\limits_{l = 1}^{k_{t}}T_{i}^{t}}{k_{t}}.}}} & (16)\end{matrix}$As such, the “friendliness” ratio can be defined as:F=T_(M)/T_(T).  (17)

To verify “rate smoothness” for the MSTFP protocol connections, letR_(m) _(i) ¹, R_(m) _(i) ², . . . , R_(m) _(i) ^(Sm) represent thesending rates at different time instances 1, 2, . . . s_(m) of the ithMSTFP protocol connection and R_(t) _(k) ¹, R_(t) _(k) ², . . . , R_(t)_(k) ^(St) represent those of the kth TCP connection, then the sendingvariation of the MSTFP protocol connections and the TCP connections arerespectively defined as:

$\begin{matrix}{\Delta_{M_{i}} = {{\sum\limits_{j = 1}^{sm}{{{R_{m_{i}}^{j} - R_{m_{i}}^{j - 1}}}\mspace{14mu}{and}\mspace{14mu}\Delta_{T_{k}}}} = {\sum\limits_{j = 1}^{st}{{{R_{t_{k}}^{j} - R_{t_{k}}^{j - 1}}}.}}}} & (18)\end{matrix}$

The smoothness ratio is defined asS=Δ _(M) _(i) /Δ_(T) _(k) .  (19)

By way of example, when S≧1 then the kth TCP connection is smoother thanthe ith MSTFP protocol connection.

FIG. 5 shows the simulation results of the throughput as measured in Kbwith respect to time measured in seconds for six (6) differentconnections. The data points for FIG. 5 are listed in the Appendix. Twoconnections were used in an implementation of the MSTFP protocol(MSTPF1, MTPF2), two connections were the TCP protocol (TCP1, TCP2), andtwo connections (RAP1, and RAP2) were the Real time Adaptive Protocol(RAP) taught by Rejaie et al [SIGCOM]. The sending rates were measuredin bps with respect to time. The six (6) different connections areillustrated in FIG. 6. The data points for FIGS. 5 and 6 are listed inthe Appendix, below. From FIGS. 5 and 6 it can be seen that the MSTFPprotocol disclosed herein is more ‘friendly’ to TCP than RAP and alsosmoother than TCP and RAP.

The simulation used the MPEG-4 test sequence “coast guard” to illustratethe performance of the resource allocation scheme. The coast guard testsequence includes four objects—river (obj0), boat (obj1), yacht (obj2),and riverbank (obj3). The four objects were coded in CIF at a temporalresolution of 10 fps. In the simulation, the quality-impact parameterfor these objects was selected as 0.7, 1.2, 1.2, and 0.7, respectively.The bottleneck link bandwidth (kb) is set to 100, 140, 100, 80, 100,140,100, 80, 100, and 140 to respectively correspond to time (ms) 0, 500,1000, 1500, 2000, 2500, 3000, 3500, 4500, and 5000.

The test sequence plotted in FIG. 7, the data points for which arelisted in the Appendix, shows the PSNR per frame of different objects.The thick line illustrates the resource allocation control scheme andthe thin line is an illustration without the network resource allocationcontrol scheme. FIG. 7 illustrates coding at CIF 7.5 Frames Per Second(FPS) using the MPEG-4 test sequence “Coast Guard” but, for the benefitof clarity, illustrates only the simulation results of obj1 and obj3.

FIG. 8 shows plots of the PSNR per frame coded at CIF 7.5 Frames PerSecond (FPS) and using the MPEG-4 test sequence “Coast Guard”. The datapoints for FIG. 8 are listed in the Appendix, below. An implementationof the resource allocation control scheme is seen in a solid line andthe dashed line illustrates a rate control scheme without thisimplementation. Note that there are several sharp drops in the resourceallocation control scheme due to frame skipping. Furthermore, it can beseen that during the period of no frame skipping, the resourceallocation control scheme has a higher PSNR. It can be seen in FIG. 8that, even taking the skipped frames into consideration, theimplementation of the resource allocation control scheme achieves abetter video quality. The data points for FIG. 8 are listed in theAppendix, attached hereto.

Table 1 shows a comparison of the results with and without the MSTFPprotocol resource allocation scheme disclosed herein. The multiple videostreams for the MPEG-4 test sequence “coast guard” were used to producethe results seen in Table 1 for each of the four objects—river (obj0),boat (obj1), yacht (obj2), and riverbank (obj3).

TABLE 1 Resource control Average scheme Obj0 Obj1 Obj2 Obj3 PSNR MSTFP WPSNR W PSNR W PSNR W PSNR 24.16 Resource 0.7 2464 1.2 19.52 1.2 19.910.7 23.99 allocation Without control PSNR PSNR PSNR PSNR 20.99 24.2315.45 18.12 22.30

4. Network Adaptive Rate Control Scheme

An implementation of a network adaptive rate control scheme will now bepresented in conjunction with the example illustrated in FIG. 9. Also,the results of a simulation of an example of a network adaptive ratecontrol scheme are set forth.

A. Discussion

The Network Adaptive Rate Control (NARC) scheme disclosed hereinachieves minimal distortion in a global scene. Specifically, an overviewis first given of an implementation of the NARC scheme, followed by afocus upon a quantizer adjustment of the NARC scheme.

FIG. 9 shows a block diagram of the NARC scheme for multiple videoobjects (MVOs). The block diagram depicts a flow chart for thecalculation of an estimate of the MSTFP available bandwidth that is madeat module 910 of FIG. 9.

Unlike the prior art rate control schemes taught by Chiang et al. andVetro et al., implementations of the MVOs NARC scheme includes featuressuch as dynamically estimating the available bandwidth at module 910,the target rate and global buffer updating at module 912, quantizationadjustment at module 934, and frame skipping control at module 960.Functionalities of these modules are discussed below.

The MVOs NARC scheme illustrated in FIG. 9 includes five stages, each ofwhich will now be described. In the first stage, illustrated generallyat module 910, the current available network bandwidth (R_(T)) isestimated in accordance with the MSTFP protocol. Together with thenumber of bits spent in the previous time instant (B_(prev)), the size(R_(old)/2) and the occupancy (W_(prev)) of the encoder output buffer,the target rate and global buffer are then updated for each Video ObjectPlane (VOP_(i)) frame at module 912. The output total target bits fromthe joint buffer control are allocated among each Video Object Plane(VOP_(i)) at module 914 to yield the target bits for each individualobject. As the buffer size, R_(old)/2, is changed to R_(T)/2, theoccupancy of the buffer, W_(cur), is changed as follows:W _(cur)=max((W _(prev) +B _(prev))×R _(T) /R _(old) −R _(T) /F), 0,  (20)where “F” is the video frame rate (e.g., 20 frame/second, 30frame/second, etc.)

In the second stage, which is the pre-encoding part seen generally atreference numeral 930, the quantizer of each VOP_(i) is adjusted. Chianget al. teach that the relationship between the quantization parameter(QP) and the texture value can be described as

$\begin{matrix}{{r = {\frac{p_{1} \times {MAD}}{QP} + \frac{p_{2} \times {MAD}}{{QP}^{2}}}},} & (21)\end{matrix}$where p₁ and p₂ are control parameters. In the pre-coding part,initialization of the control parameters p₁ and p₂ takes place atinitialization module 932. In order to maintain a constant quality ofthe total video sequence, the QP of each VOP_(i) is limited to the rangefrom 1 to 31, depending upon the bandwidth. The QP is allowed to changewithin a pre-defined range compared with the previous QP. A QP of 1reflects the best quality and 31 represents the worst quality.

The Quantization Adjustment module 934 performs functions thatcontribute towards a global reduction in distortion. To achieve theglobal minimal distortion among the MVOs, the implementation of the MVOsNARC scheme employs the quadratic function to predict the number ofbits, r_(i), which will be used to encode the ith MOP:

$\begin{matrix}{r_{i} = {\frac{\left( p_{1} \right)_{i} \times {MAD}_{i}}{{QP}_{i}} + {\frac{\left( p_{2} \right)_{i} \times {MAD}_{i}}{{QP}_{i}^{2}}.}}} & (22)\end{matrix}$

Still another quadratic function proposed by Chiang et al. is used toestimate the distortion, and is given by:d _(i)=(q ₁)_(i) ×QP _(i)+(q ₂)_(i) ×QP _(i) ².  (23)where q₁ and q₂ are control parameters.

Verscheure et al. teach that packet-loss has an impact on video quality.A rate control implementation disclosed herein takes into considerationthe packet-loss that occurs during video transmission. Video qualitydeteriorates quickly as the packet-loss rate and the sending rate go up.

To take the packet-loss into account, Eq. (23) is modified to:d _(i)=(q ₁)_(i) ×QP _(i)+(q ₂)_(i) ×QP _(i) ²+(q ₃)_(i) ×r _(i)×(P_(L))_(i),   (24)where q₃ is the additional control parameter.

The objective of a rate control is to minimize the overall distortion toobtain the optimized quality for the whole video frame. Such aminimization can be expressed as:

$\begin{matrix}{{{{minimize}\mspace{14mu} D} = {\sum\limits_{i}d_{i}}},{{{subject}\mspace{14mu}{to}\mspace{14mu} R} = {{\sum\limits_{i}r_{i}} \leq R_{T}}},} & (25)\end{matrix}$where R_(T) is the total bit budget for the current time instantobtained from the buffer control algorithm and the MSTFP protocol. Thethird stage, seen generally in FIG. 9 at reference numeral 940, performsan encoding process based upon the quantization parameter (QP) estimatefrom the second stage, above. The “Intra coding” at module 944 receivesthe QP from pre-encoding Quantization Adjustment module 934 and isdirected to the I-picture frame. The Quantization Adjustment module 934is discussed further below. The “Inter coding” at module 942 receivesinitialized values from a pre-coding initialization module 932 and isdirected to the P-picture frame or the predicted picture. Both “Intracoding” module 944 and the “Inter coding” at module 942 pass I-pictureframes and P-picture frames, respectively, to the post encoding fourthstage seen generally at reference numeral 952 in FIG. 9.

In the fourth stage, the rate model is updated at module 954. Theobjective of a rate control is to minimize the overall distortion. Theupdate to the distortion model is performed at module 956. The rate anddistortion models are updated based on the encoding results of thecurrent frame as well as those from a specified number of the previousframes. Both the rate and the distortion aspects of the rate anddistortion models are functions of the quantization parameter (QP) fromEq. 21 and the probability that the trace is in the loss state (P_(L))from Eq. 4. The update to the rate and distortion models can be doneusing the least squares procedure described by Eckert et al.

The fifth stage is a frame skipping module 960 in FIG. 9. In the fifthstage, frame skipping occurs after all the video objects (VOs) in thescene have been encoded. Frame skipping occurs at this point in theimplementation because, when the global scene is considered, all the VOscomposed within the same scene should be encoded at the same frame rate.For the purpose of frame skipping, the P-picture frame has a lowerpriority and the I-picture frame has a high priority. As such, theP-picture frame will preferably be the frame that is chosen to beskipped.

B. Simulation Results

To illustrate the bandwidth adaptation ability of an implementation ofthe NARC scheme, a simulation was conducted of the MSTFP protocol usingthe Network Simulator (NS) software version 2. The results of thesimulation are illustrated in FIG. 10 and the data points therefore arelisted in the Appendix. FIG. 10, discussed below, demonstrates thatgiven a variable available bandwidth, the MSTFP protocol can dynamicallyadjust the sending rate to match up with the available networkbandwidth.

FIG. 10 depicts the available network bandwidth and its estimation inplot of bandwidth measured in kbps against time measured in ns. Theavailable network bandwidth is illustrated in FIG. 10 as a dashed lineand the MSTFP estimated network bandwidth is illustrated by a solidline.

In the simulation, a standard MPEG-4 codec was used with unrestrictedmotion vector modes. The simulation tested two rate control schemes: 1)the bandwidth adaptive MVOs rate control scheme disclosed herein, and 2)a conventional MPEG-4 standard MVOs rate control (Q2) without anyfeedback from network bandwidth and packet-loss rate. A change was madein the frame skipping part of the conventional MPEG-4 Q2 scheme so as tomaintain all the objects of the same scene in a consistent frame rate.In both cases, the first frame was intracoded, and the remaining frameswere interceded. The tests used the MPEG-4 “coast guard” video testsequence and the MPEG-4 “news” test video sequences, respectively. Bothof them are composed of four video objects.

PSNR was used in the simulation as a metric to measure video quality.For an eight-bit image with intensity values between 0 and 255, the PSNRis given by:

$\begin{matrix}{{{PSNR} = {20\;\log_{10}\frac{255}{RMSE}}},} & (26)\end{matrix}$where RMSE stands for root mean squared error. Given an original N×Mimage f and a compressed or degraded image f′, the RMSE can becalculated as follows:

$\begin{matrix}{{RMSE} = \sqrt{\frac{1}{N \times M}{\sum\limits_{x = 0}^{N - 1}{\sum\limits_{y = 0}^{M - 1}{\left\lbrack {{f\left( {x,y} \right)} - {f^{\prime}\left( {x,y} \right)}} \right\rbrack^{2}.}}}}} & (27)\end{matrix}$

A fair comparison of PSNR between the two rate control methods with theskipping of different frames is not trivial. A rate control techniquethat skips more frames would typically spend more bits per coded frameand could easily have a very high average PSNR per coded frame. Table 2,below, presents the rate control impact on video quality. The averagePSNRs of the encoded frames are shown in the third column of Table 2. Itcan be seen from Table 2 that there is more frames skipping in theconventional MPEG-4 Q2 scheme than in an implementation of the NARCscheme.

TABLE 2 Rate Encoded Video control average Total average Sequence schemePSNR Skipped frame PSNR Coast guard NARC 26.02 20 23.92 (~100 kbps)scheme MPEG-4 27.33 26 21.89 Q2 scheme News NARC 30.97 8 30.77 (~100kbps) scheme MPEG-4 33.08 25 29.36 Q2 scheme

Table 2 also demonstrates that the encoded average PSNR in theconventional MPEG-4 Q2 scheme is higher than in the NARC scheme.However, using the encoded average PSNR value as a measure of compressedvideo quality is not accurate. This is because the distortion of thenon-encoded video is not taken into account. In the rate-control testingin the conventional MPEG-4 Q2 scheme, it was decided that when a framewas skipped, the previous encoded frame should be used in the PSNRcalculation because the decoder displays the previous encoded frameinstead of the skipped one. The average PSNR is calculated using thisapproach herein and the results are shown in Table 2 as the “TOTALaverage PSNR” in column 5.

FIGS. 11 and 12 each show a plot of PSNR per frame at 10 frames persecond, where FIG. 11 uses the MPEG-4 “coast guard” test sequence andFIG. 12 uses the MPEG-4 “news” test sequence. The respective data pointsfor each of FIGS. 11 and 12 are listed in the Appendix. In FIGS. 11 and12, the solid line illustrates an implementation of the NARC scheme andthe dashed line illustrates the convention MPEG-4 Q2 scheme. The PSNRvalues of the tested video drops sharply due to frame skipping. FIGS. 11and 12 illustrate that the NARC scheme significantly reduces the numberof frames that are skipped. During the period when no frames are skippedin either method, the NARC scheme has a higher PSNR, and therefore videoquality, than that of the conventional MPEG-4 Q2 scheme. This is becausethe packet-loss rate in the NARC scheme is less than that in theconventional MPEG-4 Q2 scheme.

The above-described implementations of systems and methods are presentedherein in the general context of server-client architecture via theInternet. The client and server may be implemented by general-purposecomputers, or by other particularly tailored computing devices, such asminicomputers, mainframe computers, workstations, Internet appliances,set top boxes, wireless communication devices, game consoles, portablecomputing devices, and the like.

An exemplary computer system has one or more processors, memory, and oneor more input/output (I/O) devices. The processor communicates with thememory and I/O devices via one or more bus/interface mechanisms.Programs, data, files, and the like may be stored in memory and executedon the processor.

The memory typically includes both volatile memory (e.g., RAM) andnon-volatile memory (e.g., ROM, Flash, hard disk, CD-ROM, DVD, etc.).Examples of possible I/O devices include a mouse, a touch pad, ajoystick, a keyboard, a keypad, a display, a peripheral storage device,and a microphone. The computer system may also implement a computeroperating system that is stored in memory and executed on the processor.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A computer system for transmitting a mixed media data stream inpackets, including audio and video objects, between a sender and areceiver through a connection over a network, the computer systemadapted to implement a method comprising: monitoring, at the receiver,transmission characteristics of the connection between the server andthe receiver; estimating available bandwidth at the sender based uponthe transmission characteristics of the connection monitored at thereceiver; allocating a global buffer for the mixed media data stream tobe transmitted from the sender to the receiver as a function of theestimated available bandwidth at the sender; pre-encoding a portion ofeach Video Object Plane (VOP) in the global buffer with respect to aquantization parameter (QP) of the VOP; encoding the VOP in the globalbuffer based on the QP; updating a rate distortion model based upon theQP and packet loss rate; performing a frame skipping function after theVOP encoding; and transmitting from the sender to the receiver theencoded video object plane in the global buffer at a regulated sendertransmission rate from the sender as a function of the estimatedavailable bandwidth at the sender; wherein pre-encoding a portion ofeach VOP with respect to the QP of the VOP further comprises adjustingthe QP of the VOP; and wherein the QP of the VOP is adjusted withrespect to a texture parameter, r, as the number of bits which will beused to encode the VOP wherein:${r = {\frac{p_{1} \times {MAD}}{QP} + \frac{p_{2} \times {MAD}}{{QP}^{2}}}};$p₂ and p₂ are control parameters; and MAD is a mean absolute distortionin which a total target bit rate for all objects in the global bufferare allocated proportionally to motion, size, and square of MAD.
 2. Thecomputer system as defined in claim 1, wherein the method implemented bythe computer system further comprises: receiving the encoded videoobject plane at the receiver from the connection; demultiplexing theencoded video object plane into coded video and audio streams; inputtingthe coded video and audio streams, respectively, into video and audiodecoders; inputting the decoded video and audio streams to a mediamixer; and inputting the mixed video and audio streams output from themedia mixer to an output device.
 3. The computer system as defined inclaim 1, wherein the adjusting of the QP of the VOP is performed bychanging the QP to a values in a range from 1 to 31 depending upon theestimated available bandwidth at the receiver.
 4. The computer system asdefined in claim 1, wherein the computer system comprises at least oneof (i) one or more servers or (ii) one or more clients.
 5. A computersystem for transmitting a mixed media data stream in packets, includingaudio and video objects, between a sender and a receiver through aconnection over a network the computer system adapted to implement amethod comprising: monitoring, at the receiver, transmissioncharacteristics of the connection between the server and the receiver;estimating available bandwidth at the sender based upon the transmissioncharacteristics of the connection monitored at the receiver; allocatinga global buffer for the mixed media data stream to be transmitted fromthe sender to the receiver as a function of the estimated availablebandwidth at the sender; pre-encoding a portion of each Video ObjectPlane (VOP) in the global buffer with respect to a quantizationparameter (QP) of the VOP; encoding the VOP in the global buffer basedon the QP; updating a rate distortion model based upon the QP and packetloss rate; performing a frame skipping function after the VOP encoding;and transmitting from the sender to the receiver the encoded videoobject plane in the global buffer at a regulated sender transmissionrate from the sender as a function of the estimated available bandwidthat the sender; and wherein: the sender sends data to the receiver inthrough a connection over a packet switched network in a sender packethaving a sender header that includes: a packet sequence number; atimestamp indicating the time when the sender packet was sent (ST1); andthe size of the sender packet (PacketSize); the receiver sends data tothe sender through the connection over the packet switched network in areceiver packet having a receiver header that includes: the timeinterval that the sender packet spent in the receiver side (ΔRT); thetimestamp of the sender packet sent from the sender (ST1); an estimate,calculated by the receiver, of a packet-loss rate; and the rate at whichdata is received at the receiver; monitoring transmissioncharacteristics of the connection between server and receiver comprises:estimating a round trip time of the sender packet from the sender to thereceiver (RTT) based on ST1 and ΔRT; estimating a time out interval (TO)before which the sender should retransmit to the receiver a senderpacket of data that has not been received by the receiver; estimating aprobability that a packet of data will be lost (P_(L)); estimating thepresent available network bandwidth at which the receiver can receivedata from the sender (rvcrate) as a function of the PacketSize, the RTT,the P_(L), and the TO; deriving the present sending rate of data fromthe sender to the receiver ( currate); setting an updated sending rateof data from the sender to the receiver (currate), wherein: if rcvrateis greater than currate, then deriving currate as a function currate,PacketSize, and RTT; and if rcvrate is not greater than currate, thensetting currate to be less than rcvrate; and wherein:RTT=α× RTT +(1−α)×(now−ST1−ΔRT); and now is the timestamp indicating thetime at which the receiver packet was received in the sender; and a is aweighting parameter.
 6. The computer system as defined in claim 5,wherein the computer system comprises at least one of (i) one or moreservers or (ii) one or more clients.
 7. A computer system fortransmitting a mixed media data stream in packets, including audio andmultiple video objects (MVOs), between a sender and a receiver through aconnection over a network, the computer system adapted to implement amethod comprising: monitoring transmission characteristics of one ormore encoded video object planes through the connection between thesender and the receiver; estimating, from the transmissioncharacteristics, an available bandwidth (RT) at the sender; allocating,as a function of the RT, a portion of the mixed media data stream to aglobal buffer; encoding a video object plane from the global bufferbased upon a rate distortion function that accounts for packet loss ratebetween sender and receiver; updating the rate distortion function basedupon results of the encoded video object plane and upon a memorycontaining results of one or more previously encoded video objectplanes; after the encoding the MVOs in the video object plane,performing a frame skipping function; and transmitting, at the estimatedavailable bandwidth, the encoded video object plane from the sender tothe receiver; wherein allocating a portion of the mixed media datastream to a global buffer comprises:W _(cur)=max(((W _(prev) +B _(prev))×R _(T) /R _(old) −R _(T) /F), 0) asthe global buffer size R _(old)/2, is changed to R _(T)/2, wherein:B_(prev) is the number of bits spent in the previous time instantB_(prev), R_(old)/2 is the previous size of the global buffer; W_(prev)is the previous occupancy of the global buffer; and F is the video framerate.
 8. The computer system as defined in claim 7, wherein allocating aportion of the mixed media data stream to a global buffer comprises theallocation of an output target rate from the global buffer among each ofvideo and audio data streams so as to yield the target bits for anindividual object in the data stream.
 9. The computer system as definedin claim 7, wherein the method implemented by the computer systemfurther comprises: receiving the encoded video object plane at thereceiver from the connection; demultiplexing the encoded video objectplane into coded video and audio streams; inputting the coded video andaudio streams, respectively, into video and audio decoders; inputtingthe decoded video and audio streams to a media mixer; and inputting themixed video and audio streams output from the media mixer to an outputdevice.
 10. The computer system as defined in claim 7, wherein thecomputer system comprises at least one of (i) one or more servers or(ii) one or more clients.